1. Field of the Invention
The present invention relates to a method for optically encoding digital data in the form of logic bits of binary data in cells along a track on a substrate and the data record carrier formed thereby. More specifically, the present invention relates to the storing of digital data in cells having specific dimensions with the stored data in each cell being in the form of an optical transition or non-transition in the cell and with the cells being located in arcuate tracks of equal radii that are arranged in an equally spaced, nested array.
2. Description of the Prior Art
Heretofore it has been proposed in U.S. Pat. No. 4,213,040 to encode digital information in rows and columns on a record carrier. Data is read from the record carrier by movement of the record carrier on an X axis and rotation transport mechanism which is operable to make skew corrections.
Also heretofore various optical encoded data record carriers and optical "writers" and "readers" have been proposed. For example, in U.S. Pat. No. 3,549,897 there is disclosed an absolute electro-optical encoder for indicating the angular position of a shaft. The encoder includes a stationary disc and a rotary disc, the discs having concentric tracks with transmissive and non-transmissive portions which are binarily related. Light passing through the discs is picked up by certain selected combinations of photocells for indicating the position of one disc relative to the other disc.
In U.S. Pat. Nos. 3,501,586; 3,624,284; 3,885,094; 3,795,902; 3,806,643; 3,891,794; 4,090,031 and 4,163,600 issued to J. Russell, various "writers" and "readers" are disclosed for "writing" digital data on a spiral track and for "reading" digital data from the spiral track. In the optical encoding and decoding systems described in these patents opaque spots on the track correspond to logic 1 bits of binary data and transparent spots on the track correspond to logic 0 bits of binary data. Also, larger synchronization spots are provided at different places along the track.
An apparatus for scanning a data record medium is disclosed in U.S. Pat. No. 3,898,629 wherein binary digital information is recorded in the form of data along a circular arc and a plurality of such circle arcs of data information are arranged tightly adjacent each other.
In U.S. Pat. No. 3,919,697 there is disclosed a data record having track lines which may be separate parallel tracks or may be a single series track of the spiral or raster type.
In U.S. Pat. No. 3,983,317 there is disclosed an astigmatizer for a laser recording and reproducing system. In this system concentric circular tracks are formed in a thermoplastic record or disc by burning selected holes through the disc with a laser. The laser is "on" while the disc is being rotated a short distance to form an elongate data information bit in the track. Then, in reading the data the laser beam or spot is elongated in a direction transverse to the direction of the track with an astigmatizer unit so that a small elongate beam of light with an axis extending transverse to the axis of the track and of the elongate opening therein is used to read the opening.
In U.S. Pat. No. 4,094,010 there is disclosed an optical multi-channel digital disc storage system. Data is stored on a spiral information track and holes corresponding to the information data are burned into the material of the disc by an information radiation beam.
U.S. Pat. No. 4,094,013 discloses an optical storage disc system with disc track guide sectors wherein the data tracks are spiral shaped turns or concentric turns on the disc. The data stored is again in the form of holes burned into the disc.
U.S. Pat. No. 4,209,804 discloses a record carrier containing information in an optically readable radiation reflecting information structure. With the record carrier of this patent, data is stored in a spiral track on a disc in the form of information areas comprising pits pressed into the record carrier surface or hills projecting from the record carrier surface. According to the teachings of this patent, the depth of the pits or the height of the hills is constant and so is the width of the information areas and intermediate areas at the level of the plane of the lands. Then the information to be conveyed by the record carrier is contained in the variation of the structure of the areas in the tangential direction only. More specificially, the information areas are substantially V-shaped, the phase depth of each information area having one value between 100.degree. and 120.degree. and the angle of inclination between the walls of the information areas and normal to the record carrier are substantially constant and have a value between 65.degree. and 85.degree..
As will be described in greater detail hereinafter, the present invention differs from the record media and carriers disclosed in the prior art patents referred to above by providing a method for optically encoding binary/digital data on a substrate of a record carrier wherein the data cells containing bits of data are closely compacted by having the data stored in each data cell in the form of an optical transition or non-transition over the length of the cell in arcuate data tracks all having the same radius and being arranged in a nested, equally spaced apart array of tracks which are non-spiral and where the tracks are not arcs of concentric circles. The non-transition cells are cells which are completely transmissive or completely non-transmissive in one embodiment or completely reflective or completely non-reflective in another embodiment. The transition cells are partially transmissive and partially non-transmissive in one embodiment and partially reflective and partially non-reflective in another embodiment.
The change in transmissiveness or reflectance occurs in a direction along the length of the cells and in the direction of the track such that there is a transition as a scanning or reading head comprised of a light source and a light sensor which picks up transmitted or reflected light travels along the length of the track.
The simple method disclosed herein for optically encoding data on a substrate and the data record carrier formed thereby enable one to compact data very closely on the track and such data encoding is highly tolerant of noise, i.e., in the sharpness or fuzziness of the cell edge, to the location of the edge of a cell or to the position of a transition within a cell.
Typically, the non-occurrence of a transition over the length of a cell on a track corresponds to a logic 0 bit of information and the occurrence of a transition across the length of the cell corresponds to a logic 1 bit of information, it being understood that the reverse encoding or decoding will work as well.
Further, a plurality of arcuate tracks of the cells are created on the substrate with each track being spaced from an adjacent track by a predetermined distance at a point intermediate the ends of each track, and each track has the same radius throughout the arcuate path of the tracks such that the tracks extend in an arcuate manner across the data record carrier with each track having the same radius and being arranged in a nested manner relative to adjacent tracks along a common centerline.